Support with integrated deposit of gas absorbing material for manufacturing microelectronic microoptoelectronic or micromechanical devices

ABSTRACT

The specification teaches a device for use in the manufacturing of microelectronic, microoptoelectronic or micromechanical devices (microdevices) in which a contaminant absorption layer improves the life and operation of the microdevice. In a preferred embodiment the invention includes a mechanical supporting base, and a layer of a gas absorbing or purifier material is deposited on the base by a variety of techniques and a layer for temporary protection of the purification material is placed on top of the purification material. The temporary protection material is compatible for use in the microdevice and can be removed during the manufacture of the microdevice.

REFERENCE TO OTHER RELATED DOCUMENTS

This patent application is related to co-pending U.S. application______, filed Jul. 19, 2002, entitled SUPPORT FOR MICROELECTRONIC ANDMICROMECHANICAL DEVICES, which is hereby incorporated by reference inits entirety for all purposes, this application claims priority under 35U.S.C. 119 to Italian Applications MI-2001-A-001557, filed Jul. 20, 2001and MI-2002-A-000689 filed Apr. 2, 2002, both of which are incorporatedby reference in their entirety for all purposes.

BACKGROUND

The present invention relates to a support for manufacturingmicroelectronic, microoptoelectronic or micromechanical devices withintegrated deposit of gas absorbing material.

Microelectronic devices (also called integrated electronic circuits, orICs) are the base of the integrated electronics industry.Microoptoelectronic devices comprise, for example, new generations ofinfrared radiation (IR) sensors which, unlike traditional ones, do notrequire cryogenic temperatures for their operation. These IR sensors areformed of an array of semiconductor material deposits, for examplesilicon, arranged in an evacuated chamber. Micromechanical devices(better known in the field under the definition “micromachines” orreferred herein as MMs) are being developed for applications such asminiaturized sensors or actuators. Typical examples of micromachines aremicroaccelerometers, which are used as sensors to activate automobileairbags; micromotors, having gears and sprocket wheels of the size of afew microns (μm); or optic switches, wherein a mirror surface on theorder of a few tens microns can be moved between two differentpositions, directing a light beam along two different directions, onecorresponding to the “on” condition and the other to the “off” conditionof an optical circuit. In the following description, these devices willalso all be referred to within the general definition of solid-statedevices.

ICs are manufactured by depositing layers of material with differentelectric (or magnetic) functionalities on a planar then selectivelyremoving them to create the device. The same techniques of depositionsand selective removal create microoptoelectronic or micromechanicaldevice construction as well. These devices are generally contained inhousings formed, in their turn, with the same techniques. The supportmost commonly used in these productions is a silicon “slice” (usuallyreferred to as a “wafer”), about 1 mm thick and with a diameter up to 30cm. On each of these wafers a very high number of devices may beconstructed. At the end of the manufacturing process individual devices,in the case of micromachines, or part, in the IR sensor case, areseparated from the slices using mechanical or laser means.

The deposition steps are carried out with such techniques as chemicaldeposition from vapor state, (“Chemical Vapor Deposition” or “CVD”); orphysical deposition from vapor state (“PVD”, or “Physical VaporDeposition”) The latter is commonly known in the art as “sputtering.”Generally, selective removals are carried out through chemical orphysical attacks using proper masking techniques, and such techniquesare well-known in the field and will not be discussed here except asthey relate specifically to the invention.

The integrated circuits and the micromachines are then encapsulated inpolymeric, metallic or ceramic materials, essentially for mechanicalprotection, before being put to final use (within a computer, anautomobile, etc.). In contrast, IR radiation sensors are generallyencapsulated in a chamber, facing one wall thereof”, transparent to theIR radiation and known as a “window.”

In certain integrated circuits it is important to be able to control thegas diffusion in solid state devices. For example, in the case offerroelectric memories, hydrogen diffuses through the device layers andcan reach the ferroelectric material, which is generally a ceramicoxide, such as lead titanate-zirconate, strontium-bismuth tantalate ortitanate, or bismuth-lanthanum titanate. When the hydrogen reaches theferroelectric material, it can alter its correct functioning.

Still more important is gas control and elimination in IR sensors and inmicromachines. In the case of IR sensors, the gases which may be presentin the chamber can either absorb part of the radiation or transport heatby convection from the window to the array of silicon deposits, alteringthe correct measurement. In the case of micromachines, the mechanicalfriction between gas molecules and the moving part, due to the verysmall size of the latter, can lead to detectible deviations from thedevice's ideal operation. Moreover, polar molecules such as water cancause adhesion between the moving part and other parts, such as thesupport, thus causing the device's failure. In the IR sensors witharrays of silicon deposits or in the micromachines, it is thereforefundamental ensure the housing remains in vacuum for the whole devicelife.

In order to minimize the contaminating gas in these devices, theirproduction is usually conducted in vacuum chambers and pumping steps areperformed before the packaging. However, the problem is not completelysolved by pumping because the same materials which form the devices canrelease gases, or gases can permeate from outside during the devicelife.

To remove the gases entering in solid state devices during their lifethe use of materials that can sorb these destructive gases may behelpful. These absorptive materials are commonly referred to as“getters,” and are generally metals such as zirconium, titanium,vanadium, niobium or tantalum, or alloys thereof combined with othertransition elements, rare earths or aluminum. Such materials have astrong chemical affinity towards gases such as hydrogen, oxygen, water,carbon oxides and in some cases nitrogen. The aborptive materials alsoinclude the drier materials, which are specifically used for moistureabsorption, which usually include the oxides of alkali or alkaline-earthmetals. The use of materials for absorbing gases, particularly hydrogen,in ICs, is described for instance in U.S. Pat. No. 5,760,433, by Rameret. al. Ramer teaches that the chemically reactive getter material isformed as part of the process of fabricating the integrated circuit. Theuse of getters in IR sensors is described in U.S. Pat. No. 5,921,461 byKennedy et. al. Kennedy teaches that a getter is deposited ontopreselected regions of the interior of the package. Finally, the use ofgas absorbing materials in micromachines is described in the article“Vacuum packaging for microsensors by glass-silicon anodic bonding” byH. Henmi et al., published in the technical journal Sensors andActuators A, vol. 43 (1994), at pages 243-248.

The above references teach that localized deposits of gas absorbingmaterials can be obtained by CVD or sputtering during solid-state deviceproduction steps. However, this procedure can be costly and timeconsuming if done during the solid-state manufacturing CVD or sputteringprocess. This is because gas absorbing material deposition during deviceproduction implies the step involved in localized deposition of the gasabsorbing or getter material. This is generally carried out through thesteps of resin deposition, resin local sensitization through exposure toradiation (generally UV), selective removal of the photosensitizedresin, gas absorbing material deposition and subsequent removal of theresin and of the absorbing material thereon deposed, leaving the gasabsorbing material deposit in the area in which the photosensitizedresin had been removed. Moreover, depositing the gas absorbing materialin the production line is disadvantageous because there are an increasednumber of steps required in the manufacturing process. Increasedeposits, in turn, require that more materials be used, which alsosignificantly increases the risk of “cross-contamination” among thedifferent chambers in which the different steps are carried out. Also,there is a possible increase of waste products because of contamination.

SUMMARY

The present invention solves some of the above-described problems of theprior art and, in particular, simplifies the manufacturing process forsolid-state devices. The present invention includes a device for use inmanufacturing microelectronic, microoptoelectronic or micromechanicaldevices (herein also referred to as ‘microdevices’) with an integrateddeposit of gas absorbing or purification material. In one embodiment,the invention is formed of a base which includes the function of amechanical backing, a continuous or discontinuous deposit of a gasabsorbing material on a surface of said base, and a layer totallycovering said gas absorbing material deposit, made with a materialcompatible with the production of microelectronic, microoptoelectronicor micromechanical devices or parts thereof. The invention shares manyof the same manufacturing properties as standard silicon wafers or othersemiconductor materials and therefore can be used in many of the samemanufacturing processes as these materials.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described below with reference to the drawings inwhich:

FIG. 1 shows a perspective, partially cut-out view of a first possibleembodiment the invention as a support;

FIG. 2 shows a perspective, partially cut-out view of a second possiblesupport according to the invention;

FIG. 3 shows a cross section of one embodiment of the invention torepresent a particular final end product using an embodiment of theinvention;

FIG. 4 is a single microdevice as cut from the full support;

FIG. 5 shows an alternate embodiment of the invention for use withmicromechanical devices with a channel to the purification material;

FIG. 6 shows the alternate embodiment in FIG. 5 with a covering layer;

FIG. 7 shows a second alternate embodiment of the invention;

FIG. 8 is another alternate embodiment of the invention where themanufacturing layer of FIG. 2 has passages cut into it;

FIG. 9 is another alternate embodiment of the invention for use in amicromechanical device;

FIG. 10 is the individual microdevice shown from FIG. 9.

DETAILED DESCRIPTION

For purposes of clarity, the drawings show supports as represented withan exaggerated height-diameter ratio. Such exaggerations are forillustration purposes only and are not intended to reflect anyparticular limitations on the actual dimensions of the invention.Moreover, in the drawings supports are always represented with a wafergeometry, that is a low-disk of material, because this is the geometrycommonly adopted by the producers of solid state devices, but suchgeometry could be also different without departing from the scope of theinvention, for example square or rectangular.

Referring now to FIG. 1, a partially cut-out view of a first embodimentof the invention, a support for use in the manufacture of a microdevice,is shown. The support 10 includes a base layer 11. One of the functionsof the base layer 11 includes the function of mechanical backing of theentire support 10 and the devices which are subsequently manufactured onit. The thickness of the support 10 is generally on the order of onemillimeter and is nearly comprised entirely from the thickness of thebase layer 11. In one embodiment of the present invention on the surface12 of the base layer 11 there is a continuous intermediate layer 13 of agas absorbing or cleansing (also referred to herein as purification)material, 14, whose upper surface is covered with a manufacturing layer15, which is generally a substrate material 16 compatible with anintegrated circuit or micromechanical device production process, bothembodiments which are produced on the upper surface 17 of themanufacturing layer 15. The material of the base layer 11 can be ametal, a ceramic, a glass or a semiconductor, and is silicon in apreferred embodiment.

The purification material 14 can be any known material chosen among thematerials commonly referred to as either: (1) the getters, which arecapable of sorbing various gas molecules, and/or (2) the driers (ordrier materials), which are used specifically for moisture absorption.Although in an alternate embodiment both materials can be used, in apreferred embodiment only one of these materials is used.

In the scenario where the cleansing material 14 is solely a gettermaterial which in one embodiment is either (1) a metal chosen among thegroup of Zr, Ti, Nb, Ta, V; or an alloy among these metals or (2) amongthese and one or more elements, chosen from among Cr, Mn, Fe, Co, Ni,Al, Y, La and rare-earths, such as binary alloys Ti—V, Zr—V, Zr—Fe andZr—Ni, ternary alloys Zr—Mn—Fe or Zr—V—Fe or alloys with morecomponents. Preferred getter materials for this application aretitanium, zirconium, the alloy having weight percentage composition Zr84%-Al 16%, produced and sold by the Applicant under the trade name St101®, the alloy having weight percentage composition Zr 70%-V 24.6%-Fe5.4%, produced and sold by the Applicant under the trade name St 707®and the alloy having weight percentage composition Zr 80.8%-Co 14.2%-TR5% (wherein TR stands for a material that is selected from the followinggroup: rare-earth, yttrium, lanthanum or mixtures thereof), produced andsold by the Applicant under the trade name St 787®. A cleansing orpurification layer 13 which is a getter material layer can be obtainedon the base material layer 11 by different techniques, such asevaporation, deposition from metallorganic precursors, or by techniquesknown in the field as “laser ablation” and “e-beam deposition.” However,in a preferred embodiment, the getter material is obtained bysputtering.

In an alternate embodiment, the cleansing material 14 is one of thedrier materials. These materials are preferably chosen from among theoxides of alkali or alkaline-earth metals, which is preferably calciumoxide, CaO, which is used in a preferred embodiment as it does not posesafety or environmental problems during the phases of production, use ordisposal of devices containing it. An intermediate layer 13 of oxide maybe obtained for instance through the so-called “reactive sputtering”technique, depositing the alkali or alkaline-earth metal of interestunder an atmosphere of a rare gas (generally argon) in which a lowpercentage of oxygen is present, so that the metal is converted to itsoxide during deposition.

The intermediate layer 13 can have a thickness within the range of about0.1 and 5 μm. Thickness values lower than 0.1 μm, result in the gassorption capacity of the intermediate layer 13 being excessivelyreduced, while thickness values greater than the preferred embodiment of5 μm, requires deposition times which are extended without providing anyadditional sorption properties for the intermediate layer 13.

The manufacturing layer 15 is chosen from one of the materials which areusually used as substrate in solid-state device production. In oneembodiment, this material can be a so-called “III-V material” (forexample, GaAs, GaN or InP), but is silicon in a preferred embodiment.The manufacturing layer 15 can be obtained on the intermediate layersurface 14 by sputtering, by epitaxy, by CVD or by other techniqueswhich are well-known by those skilled in the art. The thickness ofmanufacturing layer 15 is generally less than 50 μm and within the rangeof about 1 to 20 μm in a preferred embodiment. The manufacturing layer15 performs two functions: (1) it protects the gas absorbing materialfrom the contact with gases until the purification material 14 isexposed by partial and localized removal of manufacturing layer 15, and(2) acts as an anchorage for the layers which are subsequently deposedit to construct ICs, microoptoelectronic devices or MMs. In oneembodiment, the manufacturing layer 15 can be itself the layer in whichthese microdevices are formed. For example, the moving parts of amicromachine can be obtained in the manufacturing layer 15 by removal ofsections of the layer. The upper surface of manufacturing layer 16 canalso be treated so as to modify its chemical composition, for exampleforming an oxide or a nitride.

FIG. 2 shows an alternate embodiment of the invention as representedpartially in a cut-out view, (like FIG. 1, the lateral dimensions of thevarious deposits on the base of gas absorption material are exaggeratedfor the sake of clarity and should not be considered limitations of thisalternate embodiment). The support 20 comprises a base layer 21. Inareas 22, 22′, . . . of the base layer surface 23) discrete deposits,24, 24′, . . . of a gas absorbing material 25 are formed. The discretedeposits 24, 24′, . . . are then covered with a manufacturing layer 26of substrate material 27. Base layer 21 is of the same kind and size ofbase layer 11 of support 10 in the first embodiment. Analogously,materials 25 and 27 in the alternate embodiment are respectively of thesame kind of materials 14 and 16 in the first embodiment, which aredescribed above.

Purification material deposits 24, 24′, . . . are generally as thick asintermediate layer 13 of the support 10 in the first embodiment. Thesedeposits 24, 24′, . . . are, however, discrete, and have lateraldimensions generally lower than 2000 μm in the length and widthdimensions These dimensions are variable within wide ranges depending onthe final use of the microdevice. For example, if the device taught bythe invention is expected for use in an ICs, the lateral dimensions willbe within the range of a few microns or less, while if the invention isused in MMs, these dimensions can be comprised between a few tens and aa couple of thousands of microns.

The manufacturing layer 26 has a variable thickness, which is thinner inthe areas over purification material deposits 24, 24′, . . . , andthicker in the areas cleared from these deposits. The manufacturinglayer 26 adheres to the base layer surface 23 in these areas which areclear from the purification material deposits. The thickness of themanufacturing layer 26 in the areas over the purification materialdeposits 24, 24′, . . . has the same values of manufacturing layer 15 ofthe support 10 in the first detailed embodiment, while in areas notlocated over the purification material deposits 24, 24′, . . . , itsthickness will be increased by the thickness of these deposits. To helppromote adherence, the manufacturing layer 26 can be made with the samematerial of base layer 21. In a preferred embodiment, the preferredcombination is silicon (which may include mono- or polycrystallinedepending on the manufacturing needs for the microdevice) for base layer21, and silicon grown through epitaxy for manufacturing layer 26.However, those skilled in the art would appreciate that othercombinations of appropriate materials can be used for these layers whichwould adhere to each properly, such as the family of GaAssemiconductors.

FIGS. 3 and 4 show an embodiment of the invention for use of the support10 in IC production. On the upper surface of manufacturing layer 17 ofthe support 10 as shown in the first embodiment, formed of themanufacturing layer 15 (which is made of silicon in preferredembodiment), solid-state microelectronic circuits, numbered as elements30, 30′, . . . are formed. These circuits 30, 30′, . . . are obtained)techniques which are known to those skilled in the art and do not needto be discussed here. The support 10 of the first embodiment is then cutalong dotted lines shown in FIG. 3, to obtain single ICs devices, whichis illustrated in FIG. 4, and shows an integrated circuit 40 obtained ona part of the support 10 of the first embodiment which has integrated,(which may be considered “buried”) under surface 17, an intermediatelayer of gas absorbing material 14. This intermediate layer 13 iscapable of sorbing gases, especially hydrogen, which may diffuse throughthe different layers of the device, thus preventing or reducing thecontamination of the integrated circuit 40.

In a second alternate embodiment the invention is used for micromachineproduction. On manufacturing layer surface 17 of the support areproduced structures, which are listed in FIG. 5 as micromachine elements50, 50′, . . . , which comprise the mobile parts of the micromachine.When the production of the micromachine elements 50, 50′, . . .(including leads for the electric connection of every singlemicromachine with the outside, which are not shown in the drawing) isfinished, the support is subjected to a localized removal operation ofmanufacturing layer 15, in areas of manufacturing layer surface 17 whichare cleared from said structures, thus forming passages 51, 51′, . . . ,which expose the gas absorbing material 14; then a covering element 60is placed over the treated support 10, which is shown in FIG. 6.

The covering element will be realized, generally, with the samematerials of base layer 11 and it should be made easily fixable tomanufacturing layer surface 17 (for example silicon is used in apreferred embodiment). The covering element 60 can have hollows, 61,61′, . . . , corresponding with areas wherein, on support 10, structures50, 50′, . . . , have been obtained and portions of intermediatepurification material layer 13 have been exposed. In particular, each ofthese hollows will be configured such that when support 10 and coveringelement 60 are fixed together, a space 62 is obtained wherein amicromachine element like 50, 50′, . . . , and a passage 51 givingaccess to purification material 14 are contained, so that this latter isin direct contact with the space 62 and is able to sorb gases which maybe present or released during time into the space 62. Finally, singlemicromachines are obtained by cutting the assembly made up of support 10and element 60 along their adhesion areas.

In another alternate embodiment of the invention, during themicromachine production process summarized above, the localized removalof manufacturing layer 15 is carried out before the manufacturing stepsof the micromachine elements 50, 50′,

FIG. 7 illustrates yet another embodiment of the invention which is madeby a variation of the process outlined above. In this embodiment, whichis depicted as micromachine 70, the support of the invention is used asa covering element 60. In this case, the substrate on which themicromachine is formed in a traditional manner as known by those skilledin the art, without the integrated purification (gas absorbing) layer.The support 10 of the invention is subjected to a localized removaltreatment of manufacturing layer 15, thus forming at the same time ahollow 71 constituting space 72 for housing mobile structure 73, and thepassage giving access to material 14.

FIGS. 8 and 9 illustrates the use of a support 20 in the alternateembodiment of the invention. Although only a micromachine is illustratedin this family of figures, in another alternate embodiment this canclearly be used with an integrated circuit. The alternate support 20 issubjected to a localized removal treatment of manufacturing layer 26 incorrespondence to purification material deposits 24, 24′, . . . , thusobtaining on the support passages 80, 80′, . . . , as shown in sectionin FIG. 8, ready for the sequence of steps for micromachine production.Moving micromachine structures, elements 90, 90′, . . . , are thenformed on this support. Microdevice assembly 101 is an alternateembodiment of the invention. A covering element 100 is fixed to thesupport 20, in the areas cleared from moving micromachine structures 90,90′, . . . and from passages 80, 80′, . . . , finally, by cuttingassembly 101 along lines (dotted in figure) comprised in adhesion areasbetween support 20 and element 100, the micromachine 110 shown by FIG.10 is obtained.

In the alternate embodiment of the invention which uses the support oftype 20 with the discrete getter deposits 24, 24′, . . . , the support20 must be produced with the final application in mind. This is because,in case of the micromachines, it is important to know the lateral sizeof the moving structures (50, 50′, . . . , 73 or 90, 90′. . . ) as wellas the lateral size of the hollows (61, 61′, . . . or 71) to be producednext, so the designer will be able to correctly define the lateral sizeand reciprocal distance of deposits 24, 24′, . . . . This considerationis important in order to assure that the hollows giving access to thegas absorbing material do not interfere with moving structure, but alsothat they are contained in the perimeter of space 62 or 72 wherein themicromachine is housed. This correct sizing can be carried out byobtaining, from final circuits producers, drawings, even preliminary, ofdevices to be produced on support 20.

The invention is applicable to microdevices or solid-state device of anytype which can benefit from an internally deposed gettering layer asdefined by the invention. A microdevice is described as any ofmicroelectronic, microoptoelectronic, or micromechanical device.However, any small-scale device which requires purification forcontaminants which passes through the device substrate or channels cutinto the substrate layer, which allow a purification layer to capturethese contaminants will benefit from the scope and spirit of theinvention and the invention should not be limited to only the threetypes of applications recited, but rather be defined by the claimsbelow.

1-30. (canceled)
 31. A process for manufacturing a microdevice includingthe steps of: creating a support device by deposing a purificationmaterial on a base comprising material selected from the groupconsisting of glasses, ceramics, semiconductors and metals, where saidpurification material is selected from the group of materials consistingof getter materials and drier materials; and covering said purificationmaterial by a manufacturing layer, where said manufacturing layer is asubstrate layer which may be used in the manufacture of saidmicrodevice.
 32. The process for manufacturing a microdevice as recitedin claim 31, comprising the additional step of creating an integratedcircuit on said manufacturing layer.
 33. The process for manufacturing amicrodevice as recited in claim 31, comprising the additional step ofcreating a micromechanical device on said manufacturing layer.
 34. Theprocess for manufacturing a microdevice as recited in claim 31,comprising the additional step of creating an IR sensor device on saidmanufacturing layer.
 35. The process for manufacturing a microdevice asrecited in claim 31 further comprising the steps of: removing selectedmaterials in said manufacturing layer, such that a cavity is created insaid manufacturing layer; attaching said support device such that itcovers operational parts of said microdevice and a seal is created atthe periphery of said cavity by said support device and saidmicrodevice, whereby said operational parts are placed in said cavityfrom removed layer of manufacturing material.
 36. The method ofmanufacturing a microdevice as recited in claim 31, wherein saiddeposing step is selected from the group consisting of: evaporation,deposition from metallorganic precursors, laser ablation and e-beamdeposition.
 37. The method of manufacturing a mircodevice microdevice asrecited in claim 31, where said deposing step is performed bysputtering.
 38. (canceled)
 39. (canceled)
 40. (canceled)